Research Topic

Surfaces & Corrosion

Surfaces & Corrosion

The project aims to study corrosion, a detrimental process with an enormous impact on global economy, by combining denstiy-functional theory calculations with thermodynamic concepts.

Corrosion

The project aims to study corrosion, a detrimental process with an enormous impact on global economy, by combining denstiy-functional theory calculations with thermodynamic concepts. [more]
We simulate the ionization contrast in field ion microscopy arising from the electronic structure of the imaged surface. For this DFT calculations of the electrified surface are combined with the Tersoff-Hamann approximation to electron tunneling. The approach allows to explain the chemical contrast observed for NiRe alloys.

FIM simulations

We simulate the ionization contrast in field ion microscopy arising from the electronic structure of the imaged surface. For this DFT calculations of the electrified surface are combined with the Tersoff-Hamann approximation to electron tunneling. The approach allows to explain the chemical contrast observed for NiRe alloys. [more]
Extremely strong (~10 V/nm) electric fields rupturing atomic bonds is a relatively well-studied concept in the field of molecular chemistry. When extended to crystalline systems, i.e. material surfaces, this concept is known as field evaporation and its exact mechanisms become more challenging to predict. Field evaporation is the central phenomenon that enables atom probe tomography (APT), and obtaining atomically-accurate APT reconstructions will be impossible without an atomically-accurate understanding of how ions initially form and depart from the surface. By performing first-principles calculations on faceted surfaces under extreme fields, we search for such an understanding.

Field Evaporation

Extremely strong (~10 V/nm) electric fields rupturing atomic bonds is a relatively well-studied concept in the field of molecular chemistry. When extended to crystalline systems, i.e. material surfaces, this concept is known as field evaporation and its exact mechanisms become more challenging to predict. Field evaporation is the central phenomenon that enables atom probe tomography (APT), and obtaining atomically-accurate APT reconstructions will be impossible without an atomically-accurate understanding of how ions initially form and depart from the surface. By performing first-principles calculations on faceted surfaces under extreme fields, we search for such an understanding. [more]
<span>The effect of surfaces and more specifically of surface reconstruction and rehybridization on the properties, composition, ordering and thermal stability of epitxailly grown alloys is investigated.</span>

Effects of surface hybridization on epitaxially grown alloys

The effect of surfaces and more specifically of surface reconstruction and rehybridization on the properties, composition, ordering and thermal stability of epitxailly grown alloys is investigated. [more]
<p>We apply our novel potentiostat approach to study the chemical reactions that take place during initial corrosion at the water-Mg interface under anodic polarization. Based on the gained insight, we derive an atomistic model that explains the origin of the anodic hydrogen evolution.</p>

Mg corrosion

We apply our novel potentiostat approach to study the chemical reactions that take place during initial corrosion at the water-Mg interface under anodic polarization. Based on the gained insight, we derive an atomistic model that explains the origin of the anodic hydrogen evolution.

[more]
ZnO is a wide band gap semiconductor which is of interest to such diverse areas of application as passivation layers on steel surfaces, catalysis, corrosion, adhesion, gas sensing, and micro- or optoelectronics. Understanding the surface structure and stoichiometry is of high practical interest and essential for any of the mentioned applications. Keeping in mind that the chemical environment interfacing with the surface plays a decisive role in the stabilisation and atomic structure of the surface reconstruction, we combine density functional theory (DFT) calculations with atomistic thermodynamics to investigate and understand the stability of polar Zn-terminated ZnO(0001) surfaces in dry and humid environment.

ZnO(0001) surfaces

ZnO is a wide band gap semiconductor which is of interest to such diverse areas of application as passivation layers on steel surfaces, catalysis, corrosion, adhesion, gas sensing, and micro- or optoelectronics. Understanding the surface structure and stoichiometry is of high practical interest and essential for any of the mentioned applications. Keeping in mind that the chemical environment interfacing with the surface plays a decisive role in the stabilisation and atomic structure of the surface reconstruction, we combine density functional theory (DFT) calculations with atomistic thermodynamics to investigate and understand the stability of polar Zn-terminated ZnO(0001) surfaces in dry and humid environment. [more]
<p>Solid-liquid interfaces are at the heart of many problems of practical importance, such as water electrolysis and batteries, photo catalytic water splitting, electro-catalysis, or corrosion. Understanding the structures forming at surfaces of solids immersed in an aqueous electrolyte is, therefore, of particularly high interest. In this project, we investigate the role the liquid environment plays in shaping such structures. We show that solvation effects are highly selective, having little effect on surfaces with metallic character, but largely stabilizing semiconducting structures, particularly those that experience a high electrostatic penalty in vacuum.</p>

Solvation of oxide surfaces

Solid-liquid interfaces are at the heart of many problems of practical importance, such as water electrolysis and batteries, photo catalytic water splitting, electro-catalysis, or corrosion. Understanding the structures forming at surfaces of solids immersed in an aqueous electrolyte is, therefore, of particularly high interest. In this project, we investigate the role the liquid environment plays in shaping such structures. We show that solvation effects are highly selective, having little effect on surfaces with metallic character, but largely stabilizing semiconducting structures, particularly those that experience a high electrostatic penalty in vacuum.

[more]
We have extended the sxdefectalign correction scheme to account for charged defects located at surfaces or interfaces. The scheme allows to extrapolate the formation energy of the defect from very small supercells, even if artificial fields in the calculation are sizeable.

Surface and interface charge corrections

We have extended the sxdefectalign correction scheme to account for charged defects located at surfaces or interfaces. The scheme allows to extrapolate the formation energy of the defect from very small supercells, even if artificial fields in the calculation are sizeable. [more]
It is very challenging to simulate within DFT extreme electric fields (a few 1010 V/m) at a surface, e.g. for studying field evaporation, the key mechanism in atom probe tomography (APT). We have developed a straight-forward scheme to incorporate an ideal plate counter-electrode in a nominally charged repeated-slab calculation by means of a generalized dipole correction of the standard electrostatic potential obtained from fully periodic FFT.

Generalized dipole correction for charged slabs

It is very challenging to simulate within DFT extreme electric fields (a few 1010 V/m) at a surface, e.g. for studying field evaporation, the key mechanism in atom probe tomography (APT). We have developed a straight-forward scheme to incorporate an ideal plate counter-electrode in a nominally charged repeated-slab calculation by means of a generalized dipole correction of the standard electrostatic potential obtained from fully periodic FFT. [more]
 
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